Hydraulic buffer



Oct. 20, 1970 R. D. RUMSEY HYDRAULIC BUFFER 4 Sheets-Sheet 1 Filed Dec.1, 1967 IAIVENIOR Qu/v 00064 ,45 Pun L55) [WW I 4 A'I [ORAL-Jo Oct. 20,1970 R. D. RUMSEY 3,

HYDRAULIC BUFFER Filed Dec. 1, 1967 4 Sheets-Sheet 2 4 Fan/M 000609504455) Filed Deb. 1, 1967 4 Sheets-Sheet 5 R 0 T A E I Pea/N 000G445Ramsay 12 ,A ATTORA/EYS United States Patent Oflice 3,534,871 PatentedOct. 20, 1970 US. Cl. 21343 24 Claims ABSTRACT OF THE DISCLOSURE Ananti-creep hydraulic railroad car draft gear buffer has a cylinder andpiston arrangement normally hydraulically locked against relativereciprocal bufiing operation. Responsive to predetermined pullout ordraft stroke force a two-way pressure relief poppet valve controllingfluid transfer passageway in the piston opens by differential pressurefluid action on the ValVe and the piston to stretch a hollow piston rodand compress a hollow valve stem anchored at its distal end within therod. Under predetermined compression or bufiing force the valve opens inresponse to fluid pressure differential acting to compressively shortenthe piston rod and stretch the valve stem.

This invention relates to hydraulic buffers and more particularlyconcerns buffers of the heavy duty, reciprocal type which are especiallyuseful in railroad car draft gear installations.

Heretofore hydraulic railroad car end draft gear has been equipped withbuffers having metering schedules which reduce the orifice area inproportion to stroke, usually in a parabolic manner, developingrelatively uniform force under impacts on the order of to 12 miles perhour. This type of draft gear performs well during humping operationsand is widely utilized on piggy-back fiat cars and auto-rack cars. Mostof these units have a buff travel of approximately 9 to 11 inches and adraft travel of 2 to 3 inches, or an average total travel ofapproximately 12 inches per car end.

In view of the fact that prior buffers have been designed to haverelatively constant force during a decelerating velocity, they aregenerally designed with relatively wide open orifices near the beginningof the stroke, and in fact, throughout most of the stroke if theschedule is parabolic. Therefore, at low closure speed or openingspeeds, such buffers are free to travel with almost no resistance. Thisfree travel occurs in the range of speeds up to 2 to 3 miles per hour.It thus becomes obvious that during train motion, if for example, 50cars in the center of the train are equipped with the prior type ofbuffer, with 12 inches of available travel per car end, there would be acapability of 100 feet variation in train length. Since each one of thebuffer units could extend or retract at a velocity, for example, of 1mile per hour, a relative speed between the front of the train and rearof the train can easily reach a level in excess of miles per hour,resulting in couplers being pulled out, or the train as a whole bucklingin the middle causing a derailment and wreck. It is strongly suspectedthat many, if not most, of recent train wrecks are attributable to thiscause.

It is, accordingly, an important object of the present invention toprovide a hydraulic buffer which overcomes the deficiencies of the priorconstructions and which will eliminate creeping in or out at lowvelocities under low load.

Another object of the invention is to provide a hydraulic buffer whichis substantially locked against extension or contraction but isresponsive to predetermined draft or buffing loads.

Another object of the invention is to provide a new and improvedhydraulic buffer which remains substantially insensitive to low velocityimpacts but is able to absorb high velocity impacts by metered hydraulicfluid displacement therein.

Still another object of the invention is to provide a hydraulic bufferespecially suitable for controlling relative movement of the cars in thetrain to safe limits.

It is a further object of the invention to provide novel control valvemeans in a hydraulic buffer utilizing the elasticity of materials tocontrol operation of hydraulic displacement valving automaticallyresponsive to internal hydraulic pressures within the buffer inoperation.

Other objects, features and advantages of the present invention will bereadily apparent from the following detailed description of a preferredembodiment thereof taken in conjunction with the accompanying drawings,in which:

FIG. 1 is a top plan view of a hydraulic bufler embodying features ofthe invention.

FIG. 2 is an end elevational view of the buffer looking from the planeof line IIlI of FIG. 1.

FIG. 3 is an enlarged fragmentary longitudinal sectional detail viewtaken substantially along the the line IIIIII of FIG. 1.

FIG. 4 is an enlarged fragmentary longitudinal sectional detail viewtaken substantially along the line IVIV of FIG. 1.

FIG. 5 is an enlarged fragmentary longitudinal sectional detail viewtaken substantially along the line V-V of FIG. 1.

FIG. 6 is an end elevational view of the piston taken substantiallyalong the line VI-VI of FIG. 4.

FIG. 7 is an enlarged fragmentary longitudinal sectional detail viewsimilar to FIG. 4 but showing the relationship of the valve and thepiston during a compression bufling stroke.

FIG. 8 is an enlarged fragmentary longitudinal sectional detail viewsimilar to FIG. 4 but showing the relationship of the control valve andthe piston during a return bufling stroke.

Although the buffer illustrated to exemplify the invention may be founduseful in numerous and varied situations wherein a substantially locked,anti-creep relationship is desired between spaced structures which mustunder predetermined load, thrust, impact, etc., conditions be permittedto move relative to one another for stress relief, the specific bufferconstruction shown is especially suited for installation in railroad carend draft gear. Therein, one of the relatively movably structures may befixedly related in a more or less rigid relation to the railroad carframe, and the other of the relatively movable structures comprises acoupler by which the associated end of the car is coupled to another caror railroad engine. In such a railroad car draft gear high pull out andimpact load forces must be resisted and accommodated by the bulfer. Forexample, a tolerable load level up to which buffing may not be needed inmodern car constructions and with modern lading techniques is on theorder of 300,000 pounds. Beyond this force level, buffing is desirable.These operating conditions are met by the buffer of the presentinvention. That is, the bulfer is so constructed and arranged that itremains substantially hydraulically locked until a predetermined forcelevel, i.e., approximately 300,- 000 pounds is reached. Thereupon,bufiing action either during a pull out or draft stroke or undercoupling thrust, sudden deceleration impact, and the like, takes placewith internal pressures within the bufler building up and automaticallyreleasing the buffer from its normally substantially hydraulicallylocked condition to effect energy-absorbing buffing displacement ofhydraulic fluid within the self-contained hydraulic system in thebuffer. Having reference to FIG. 1, S and SS represent, schematically,

spaced structures which are liable to, and under certain operatingconditions must be permitted to have relative movement toward or awayfrom one another, such as in the draft gear of a railroad car. Betweenthese structures is installed the illustrated buffer which is of therectilinear telescopically operable type including a housing ofgenerally elongated form having on one end thereof means '11 forattaching it operatively to the structure S. Extending from the oppositeend of the housing 10 is a piston rod 12 having means 13 on its outerend for attachment of the buffer to the structure SS.

Within the housing 10, the piston rod 12 has mounted on its inner end apiston 14 (FIG. 4) which is reciprocably operable within a hollowcylinder 15 which is desirably a heavy walled cylindrical tube capableof withstanding the order of magnitude of internal pressures which mustbe sustained in operation of the buffer. Desirably, mounting of thecylinder 15 within the housing 10 is such that a hydraulic fluidreservoir space 17 is provided about the cylinder by a preferablymonolithic sturdy cast housing casing 18 which is longer than thecylinder. At its end from which the piston rod 12 projects, the cylinder15 is mounted in fixed relation to the casing 18 and concentric with thepiston rod 12 by means of a combination flanged mounting fitting andpiston rod tubular bearing member 19 which is partially telescopicallyengaged within the associated end portion of the cylinder, has a lateralthrust flange 20 engaging a thrust seat 21 of the housing casing and isprovided with an outward tubular centering extension 22 which istelescoped into an end opening 23 through the casing and of largerdiameter than the outside diameter of the piston rod but of smallerdiameter than the inside diameter of the cylinder. An annular pressureseal about the piston rod 12 is provided by packing 24 within the boreof the opening 23 between the end of the flange extension 22 and apacking gland retainer flange 25 secured to the end of the casing inpacking compressing relation as by means of screws 27, with dynamiccompression on the packing by means of thrust springs 28 acting towardthe flange 25 from within the adjacent end of the flange extension 22. Aprotective dirt shield about the outwardly projecting portion of thepiston rod 12 is provided by an accordian type flexible boot 29 securedat its inner end to the flange 25 and at its outer end to the outer endportion of the piston rod.

Within the bearing member 19 a cylindrical surface 30 of substantiallength affords a stable sliding bearing for the piston rod 12. Adjacentto the inner end of the bearing surface 30 is provided an O ring dynamicseal 31 about the piston rod. To drain off hydraulic fluid that mayenter the bearing between the seal 31 and the packing 24, an annularcollection groove 32 in the bearing surface 30 communicates through aduct 33 with the reservoir 17 at the perimeter of the flange 20. Leakagepast the flange member 19 through the joint with the cylinder 15 issubstantially prevented by a sealing ring 34.

At its opposite end (FIG. 5) the cylinder 15 is mounted concentricallyrelative to the piston 14 by means of a closure flange member 35 whichhas inner end portion rabbet grooved seat 37 onto which the adjacent endof the cylinder is telescopically engaged, with a static sealing ring 38substantially preventing leakage through the joint. Concentricity of theclosure flange member 35 is maintained by telescopic entering engagementthereof within an end opening 39 in the housing casing 18 of slightlylarger diameter than the outside diameter of the cylinder 15 so as topermit assembly into the casing of the cylinder 15, the bearing flangemember 19, the piston rod 12 and the piston 14 as a unit. Attachment ofthe closure flange member to the housing casing is by means of a lateralflange 40 secured as by means of socket head cap screws 41 to theadjacent end of the casing.

In addition to its other functions, the closure flange member 35provides part of the buffer end attaching means 11. To this end, theouter end portion of the member 35 has a central integral stem 42 ofsubstantial diameter projecting from a concave bearing recess 43 whichis desirably contoured on a complementary radius to a confronting convexbearing surface 44 of a retaining nut 45 which is threadedly engagedonto the stem 43 to attach the associated end of the buffer in swiveledrelation to the structure S depicted in FIG. 1.

Operatively, hydraulic fluid such as an oil suitable for this purposefills the cylinder 15 and a substantial volume of replenising hydraulicfluid is maintained in the reservoir 17 into which there is a filleropening closed by plug 47 (FIG. 4) with an adjacent liquid level gaugefor checking purposes. Desirably a drain opening, closed by a plug 49(FIG. 5) is provided in the bottom of the head end portion of the casing18, that is, adjacent to the end closure flange 35.

According to the present invention, means are provided to ontroldisplacement of hydraulic fluid within the cylinder 15 past the pistonin such a manner as to effect a substantial normal hydraulically lockedcondition until substantially predetermined internal pressure isdeveloped within the cylinder, whereupon automatic release of the pistonfor relative telescopic bufl'lng action within the cylinder occurs.Although for some purposes it may be desired to have the automaticpressure responsive release from the locked condition operate in onlyone direction of reciprocal relative movement of the piston andcylinder, for railroad car draft gear installation, the construction andrelationship of the control device is such as to be pressureresponsively releasable in both respective directions of reciprocaloperation. To this end, the piston 14 has passageway therethroughcontrolled by valve means comprising a poppet valve member 50 which ismounted for relative reciprocal movement within the piston, but is heldnormally in fixed relation thereto by a valve stem 51 fixedly anchoredto the piston rod 12.

In a desirable construction and relationship, the valve stem 51 isfixedly secured to the valve member 50 by having an end portion of thestem telescoped into a central outwardly opening bore 52 in the valvemember and secured therein in suitable manner as by means of brazing.From the valve member, the stem 51 extends along a concentric bore 53and of a length substantially throughout the length of the pisto rod toa dead end adjacent to the outer end of the rod (FIG. 3). Adjacent tothe dead end, anchoring means desirably in the form of a pair ofcrossingly related pins 54 and 55 extend through aligned bores inaxially spaced adjacent relation in the piston rod and the valve stem,with the ends of the pins entirely within the perimeter of the pistonrod. Hydraulic fluid leakage past the anchoring pins is prevented bymeans such as O-rings 57 adjacent to their opposite ends. Endwisedisplacement of the pin 54 is prevented by a locking relation thereto ofa member 58 threadedly mounted on the outer end portion of the pistonrod 12 and comprising a coupling nut which is part of the end coupling13 and having an inner convex face 59 which is on a complementary radiusto a central outwardly opening concave recess 60 in the end face of thepiston rod, providing a swivel coupling joint with the structure SS(FIG. 1). Unintentional displacement of the member 58 from its operativecoupling head and pin-locking position on the piston rod is prevented bya staking pin 61. Endwise displacement of the anchoring pin 55 isprevented by locking means, conveniently comprising a retainer ring 62for the adjacent end of the boot 29.

For the reasons that will be presently described, the valve stem 51 isconstructed as a tube. Therefore, to strengthen the anchorage of thevalve stem to the piston rod, an anchoring plug 63 is secured within theouter end portion of the hollow valve stem and through which theanchoring pins 54 and 55 extend in a close fitting relation. For fixedattachment of the plug 63 to the valve stem, it is desirably brazedthereto. The plug 63 also provides means for drainage from the spaceafforded between the piston rod bore 53 and the valve stem through aport 64 in the valve stem wall reinforced by the plug. Within the plugis an angular passage 65 which connects the port 64 with the chamber inthe tubular valve stem. Adjacent to but spaced from the valve member 50,the space between the bore 53 and the valve stem 51 is closed by adynamic sealing ring 67 (FIG. 4) which may be of the piston ring type.

For the purposes of the present invention, the passageway through thepiston 14 and controlled by the valve 50 comprises a plurality ofbranches 68 opening through the front or head face of the piston (FIGS.4 and 6), herein shown as four in number, equally spaced apart in acircumferential direction and located on a circle intermediate the outerperimeter of the piston and a central bore 69 opening through that faceof the piston and within which the innermost end of the valve member 50is slidably received with a front end valve surface 70 exposed to thehydraulic fluid in the cylinder. Within the piston 14, the respectivepassage branches 68 extend to an annular, radially inwardly openingdistribution groove 71 at the inner end of a substantial steppedenlargement of the bore through the piston and generally aligned withthe inner end of the piston rod 12 onto which the inner end portion ofthe piston is threadedly engaged and secured against torsionaldisplacement as by means of a set screw 72. Normally, displacement ofhydraulic fluid from in front of the piston through the passage branches68 by way of the groove 71 is blocked by the valve 50 which for thispurpose has a cylindrical external control surface 73 on a maximum outerperimeter intermediate annular flange portion 74 of the valve memberslidably coacting with a complementary annular internal seat surface 75on the piston between the groove 71 and an annular radially inwardlyopening discharge groove 77 Within the piston. Communication between thegroove 77 and the back face of the piston 14 is effected through aplurality herein four, equally spaced axially extending ducts 78 in thepiston having blind ends adjacent to the groove 77 and communicatingtherewith through respective ports 79. At their outer ends, thedisplacement ducts 78 are controlled by an annular check valve 80 whichis biased by a Wavy spring 81, seated on a retainer shoulder ring 82,into closing relation to the ducts 78 to permit only rearward dischargefrom the controlled ends of the ducts and prevent return flowtherethrough.

For displacement of the hydraulic fluid from the back of the piston 14 aplurality, herein four equally spaced passageway branches 83 extendforwardly from respective check valve by-passing notches 84 into thebody of the piston on about the same diameter thereof as the ducts. 78.Interiorly of the piston the branches 83 deadend and communicate throughrespective angular ports 85 with a stepped annular discharge groove 87of smaller diameter than the discharge groove 77 and defined by anaxially extending annular internal seat 88 slidably engaged by a. fluiddisplacement blocking axially extending complementary steppedcylindrical control surface 89 of the valve member 50.

It will thus be observed that normally hydraulic fluid displacementthrough the piston 14 by way of the passageway atforded by thepassageway branches 68 and 83 and the discharge grooves in the pistonproviding part of the passageway, is completely blocked by the valve 50,so that a substantially hydraulically locked condition prevails. Therebyrelatively low magnitude or load or velocity forces imparted by thestructures S and SS during pull out or draft on the one hand orcompressive impact will be restricted without bufling action by thebuffer, thus avoiding creeping, elognation or contraction of the bufferwhich has been found undesirable when multiplied by the number ofbuffers in the draft gear of a train of railroad cars. This anti-creepfeature is controlled to function within a safe operating range, andwhen the internal hydraulic pressure on either end of the piston 14reaches a predetermined load value, the valve 50 acting as a reliefvalve meters hydraulic fluid through the piston substan tiallyproportional to pressure to effect a buffing action. This involvesrelative reciprocal movement of the valve 50 and the piston 14 which isherein automatically ac complished in response to predeterminedhydraulic operating pressures by having the piston rod 12 and the valvestem 51 serve as pressure responsive means. For this purpose, the pistonrod and the valve stem, by rea son of their tubular construction, lengthand suitable material, have suflicient elastic relative longitudinalstretching and compression ability to serve, in effect, as relief valvefuse structure. Spring tube material is used in the valve stem 51 and ofsubstantially thinner wall section and smaller diameter than the pistonrod 12, thus affording a desirable differential in stretching andcompression under the same hydraulic force, preferably amounting toabout twice the extent of elongation or shortening in length movementrelative to the piston rod.

For example, as related to a railroad car end draft gear buffer,resistance to opening of the valve 50, in either direction, may becontrolled to a force level of about 300,000 pounds. Above that forcelevel, opening of the valve 50 will progress as the force builds up toapproximately 400,000 pounds at full opening, automatically assuming theproper degree of opening incremently within the closed to full openrange proportionate to the pressure. It will be understood, of course,that the extent of relative stretching and compression of the piston rodand the valve stem must be calculated to be well within the elasticlimits of the materials for which they are respectively made.

Illustrative of the action which takes place during a compressionbuffing stroke, hydraulic pressure acts on the front or crown face ofthe piston 14 as depicted by the arrows 90 in FIGS. 4 and 7.Simultaneously, hydraulic pressure transmitted through the passagewaybranches 68 thrust against a rearwardly facing annular pressurereceiving surface 91 on the valve member 50 forwardly of the groove 71as indicated by the force arrows 92. Since the area of the surface 91 isgreater than the front end area 70 of the valve there is a forward,valve stemstretching force applied to the valve member simultaneouslywith a rearward piston rod compressing force which causes correlatedrelative axial movements of the piston and valve member'to cause thecontrol surface 73 of the valve and the seat surface 75 of the piston toseparate and provide a pressure escape relief gap to the dischargegroove 77 and thence by way of the ducts 78 and past the check valve 80to the chamber area rearwardly of the piston. Thereby closing action ofthe buffer occurs with accompanying energy absorption as the fluidescapes through the bufling metering restriction provided by the gapbetween the valve and the piston. Typically, during the bufling strOkethe piston rod -12 may compress as much as inch while the tubular valvestem rod 51 may stretch about /s inch, for a full opening of the annularbuffing metering orifice to y inch under maximum hydraulic compressionload of 400,000 pounds.

To accommodate larger volume of fluid displacement during buffing thancan be received into the working cylinder chamber back of the piston,one or more fluid by-pass ports 93 through the valve member 50 leadradially inwardly from the annular area of the discharge groove 77 tocommunication with the interior of the tubular valve stem 51 serving asan auxiliary fluid reservoir 94 (FIG. 4) and which is in communicationwith the reservoir 17 through a return tube 95 and the end closureflange 35 (FIG. 5). For this purpose the tube 95 is of a smaller outsidediameter than the inside diameter of the valve stem 51, is of a lengthgreat enough to remain in constant communication with the auxiliaryreservoir 94 throughout the range of reciprocal relative telescopicmovements of the piston 14 and the cylinder 15, and is slidably receivedthrough a central clearance bore 97 through the valve member 50 with adynamic fluid seal 98 substantially preventing pressure fluid leakagethrough the sliding joint, just as a similar dynamic seal 99substantially prevents pressure fluid leakage through the sliding jointbetween the valve member and the bore 69 in the piston.

At the end closure flange 35, the fluid return tube 95 has itsassociated end portion fixedly secured within a counterbore 100 having ablind end bore continuation 101 into the enclosure flange communicatingwith a lateral duct 102 extending to the reservoir 17 adjacent to thenear end of the cylinder 15. Thus, a continuously open return duct orpassage is provided between the reservoir 17 and the auxiliary reservoir94.

At the end of any compression buffing stroke, the annular fluiddisplacement metering orifice between the valve flange 74 and the pistoncloses by re-engagement of the valve surface 73 and the seat 75, broughtabout by return of the piston rod 12 and the valve stem 51 toward theirnormal condition, and return means function to restore the buffer to anextended, normal starting condition, even in the absence of a pull outforce applied thereto. For this purpose, a return spring 103 of thecoiled compression type is mounted about the piston rod end portion ofthe housing casing 18, with one end of the return spring thrustingagainst a shoulder 104 provided by the housing and the opposite endthrusting against a suitable abutment movable with the piston rod 12,and in this instance comprising the structure SS (FIG. 1). In a typicalexample, where the operating forces required to close the buffer are inexcess of 300,000 pounds, the spring may have a return thrust force ofon the order of 1900 pounds at neutral or starting position of thebuffer.

Return bufling is effected by metered leakage displacement of hydraulicfluid from in back of the piston 14 along its outer perimeter and pastpiston ring 105 (FIG. 4) mounted in an annular groove 107 whichintersects the passageway branches 68 and is slightly wider and deeperthan the piston ring. Through this arrangement, the piston ring has alimited range of axial displacement in the groove 107 such that duringcompression stroke it serves as a check valve against any substantialleakage from the passageway branches 68 past the outer perimeter of thepiston, but during return stroke the piston ring unseats and permitsmetered leakage displacement of hydraulic fluid from back of the pistoninto the groove 107 and past the inner perimeter of the piston ringwhich is slightly larger in diameter than the root of the groove 107. Itwill be observed that a scraper ring 108 carried by the piston 14between its crown end and respective pockets 109 of the passagewaybranches 68 opening through the outer perimeter of the pistonsubstantially precludes high pressure leakage thereby and, especiallyduring compression stroke affords a hydraulic balance for the pistonwithin the cylinder by action of the pressurized hydraulic fluid aboutthe outer perimeter of the piston between the piston ring 105 and thescraper ring 108.

In order to afford a suitable range of pullout opening of the buffer,the normal, neutral relative position of the piston 14 Within thecylinder is located a spaced longitudinal interval from the end flange19, such, for example, as about 3 inches, where a total bufling travelof the piston within the cylinder may be about l1 inches. Stopping ofpiston return at the neutral position is effected by a ring valve 110which is normally maintained by means of a coiled compression spring 111at substantially the neutral position and serves to block furtherdisplacement of hydraulic fluid around the piston when it reaches theneutral position during a return stroke and thus resumption of thenormally hydraulically locked condition of the buffer. For this purpose,the ring valve 110 is secured, as shown, to one end portion of thespring 111, and the spring is anchored at its opposite end portion, asshown, to the inner end portion of the bearing flange member 19. In itsend which engages the back of the piston, the ring valve 110 carries anannular sealing ring 112. A sealing relationship between the perimeterof the confronting perimeter of the ring valve and the wall of thecylinder 15 is effected by a piston ring 113. Through this arrangement,while the piston 14 may freely separate from the ring valve 110 during acompression or closing buffing stroke, on re-engagement of the pistonwith the ring valve 110 the return bufling stroke terminates and thehydraulically locked condition of the piston is resumed,

Hydraulic fluid which has been displaced into the reservoir 17 in thecourse of a compression bufiflng stroke, returns to the cylinder chamberfrom the gravity fed replenishing supply in the reservoir 17, by way ofthe passageway 102 in the closure flange 35 (FIG. 5) and a replenishingduct 114 leading therefrom to an annular distribution groove 115 in thebottom of a recess 117 in the inner face of the member 35. Relativelyfree replenishing displacement of hydraulic fluid by way of the groove115 under return stroke suction is permitted by unseating of a ringshaped disk valve 118 from its normally closed position over the groove115 as biased by means of a wave spring 119 held under slightcompression by a retaining flange 120 secured into the recess 117 as bymeans of screws 121. Thus, during compression strokes displacementthrough the groove 115 and the replenishing duct 114 is substantiallyprecluded by the check valve 118, but replenishing fluid is readly drawninto the cylinder chamber.

During a pullout or draft stroke force on the buffer as effected byrelative separating pull of the structures S and SS, hydraulic pressureis generated between the piston 14 and the end member 19 within thecylinder 15. This hydraulic pressure exerts an inward longitudinalforce, as indicated by the arrows 122 (FIGS. 4 and 8) on the back of thepiston 14, tending to stretch the piston rod 12. Simultaneously, thesame pressure is exerted through the passageway branches 83 and theports 85 not only inwardly on the piston 14 within the groove 87, butrearwardly against a generally axially inwardly facing annular surface123 of the valve member 50 exposed within the groove 87, as indicated byforce arrows 124, tending to compress the valve stem 51. In a typicalrailroad car end draft gear buffer, when the pullout pressure exceeds300,- 000 pounds, the piston 14 and the control valve 50 begin to moverelatively axially until the pressure separates the cylindrical valvesurface 89 from the valve seat 88 to open an annular metering orificefrom the groove 87 into the discharge groove 77, reaching a maximum opencondition at about 400,000 pounds load. At this maximum load the poppetvalve stem 51 will have been contracted by about 4; inch and the pistonrod stretched by about of an inch, for a total displacement opening ofabout inch. Hydraulic fluid thus displaced from the back of the pistonarea of the cylinder chamber escapes by way of the return tube 95 to thereservoir 17 and by way of the replenishing duct 114 to the cylinderinwardly of the piston. During pullout relief valve opening, the controlsurface 73 of the valve by reason of its substantial length maintains aclosed condition with the confronting control sur'face 75 of the piston.

Inasmuch as the pullout or draft forces are much less likely to exceedthe fuse release or pressure relief gradient in a railroad car end draftgear buffer than the compression bufling forces exerted, for example,during car coupling operations involving often severe bumping, theextent of relative pullout movement of the piston and cylinder may begenerally expected to be only partially through the pullout differentialdistance permitted from the neutral position, in any pullout forceapplication. Therefore, a slower recovery or return of the piston andcylinder to the normal neutral position after a pullout stroke may bepermitted than is desirable for recovery from a compression buffingstroke. Herein such recovery after a pullout stroke is not forced, suchas recovery after a compression stroke is forced by the return spring103, but is permitted to result from operating forces generated innormal operation wherein restricted bleeding displacement of hydraulicfluid from in front of the piston 14 through the passageway branches 68,the groove 107 and thence along the valve perimeter past the relaxedpiston ring 105 which has a split 125 for this purpose, to the rear ofthe piston until the cylinder chamber back of the piston is replenishedand the neutral position of the piston and cylinder attained.

It will be understood that variations and modifications may be effectedwithout departing from the spirit and scope of the novel concepts ofthis invention.

I claim as my invention:

1. A hydraulic buffer of the type to be mounted between two structuressubject to movement toward and away from each other and which movementshould be resisted in at least one direction, comprising:

means defining a housing having opposite ends and provided therein witha hollow hydraulic fluid cylinder between said ends;

means on one end of said housing for operative association with one ofsaid structures;

a piston reciprocably mounted in said cylinder and having a fluidtransfer passageway therethrough and a thrust surface facing in an axialdirection;

a piston rod projecting from said piston through the opposite end ofsaid housing and having an outer end;

means on said outer end of said piston rod for operative associationwith the other of said structures; and

valve means mounted in said piston to reciprocate therewith andincluding means yieldable in response to a predetermined hydraulicpressure but normally operative to positively hold said valve means inposition to close said passageway, thereby to hydraulicallysubstantially lock said piston and cylinder and restrain said movementin said one direction until said predetermined hydraulic pressure isgenerated in said cylinder, and to open in said axial direction of saidpiston thrust surface when said predetermined hydraulic pressure isgenerated and thrusts against said piston thrust surface, and a pressurethrust surface on said valve facing axially opposite to said pistonthrust surface and against which said predetermined hydraulic pressurethrusts to force said yieldable means to yield, whereby in response tothe opposite pressure thrusts on said surfaces, respectively, said valveis caused to open in said axial direction of said piston thrust surfaceto relieve the hydraulic pressure in said cylinder and permit movementin said one direction to the extent of pressure relief thus effected.

2. A hydraulic buffer according to claim 1, in which said valve meanscomprise a poppet relief valve member and said yieldable responsivemeans comprise elastic relief valve fuse structure connecting said valvemember and said piston together.

3. A hydraulic buffer according to claim 2, in which said fuse structurecomprise a valve stem fixedly related to said piston and said valvemember being mounted in relatively movable relation to the piston.

4. A hydraulic buffer according to claim 1, in which said valve meansand said piston have surfaces engaging to block fluid flow through saidpassageway, and said yieldable means comprises an elastic stem anchoredat one end to said piston rod and at the other end to said valve memberand yieldable in response to said predetermined hydraulic pressure onsaid axially facing surfaces to enable movement of the valve memberrelative to the piston to separate said normally engaging surfaces andopen said passageway thereby.

5. In a hydraulic buffer according to claim 4, said piston and saidvalve member having an angular discharge groove as part of saidpassageway therebetween, respective axially extending and radiallyfacing confronting slidably related control surfaces on said piston andsaid valve member at respective opposite sides of said groove andnormally closing said groove from the remainder of said passageway, andrespective oppositely generally axially facing pressure responsivesurfaces on said valve member within said passageway adjacent to saidcontrol surfaces normally spaced from said groove.

6. In a hydraulic buffer according to claim 5, passageway branchesleading from one end of said piston to one of said axially facingsurfaces, and passageway branches leading from the other end of saidpiston to the other of said axially facing surfaces.

7. A hydraulic buffer according to claim 1, said piston rod beingtubular, said valve member having a tubular stem, said valve stem andpiston rod being concentrically telescopically related, said meansautomatically responsive to said predetermined pressure comprisingrespectively oppositely axially facing pressure thrust surfaces on saidvalve member and said piston whereby said predetermined hydraulicpressure effects respectively opposite pressure thrust on said surfacescausing said piston rod to compress axially and said valve stem tostretch whereby to effect said opening of said valve means, andadditional respectively oppositely facing pressure responsive surfaceson said valve member and said piston reacting to predetermined hydraulicpressure in the op posite direction in said cylinder to effectcompression on said valve stem and stretching of the piston rod toeffect opening of the valve means for hydraulic pressure relief andmovement of the piston in said opposite direction.

8. A hydraulic buffer of the type to be mounted between two structuressubject to movement toward and away from each other and which movementshould be resisted in at least one direction, comprising:

.means defining a housing having opposite ends and provided therein witha hollow hydraulic fluid cylinder between said ends;

means on one outer end of said housing for operative association withone of said structures;

a piston reciprocably mounted in said cylinder and having fluid transferpassageway therethrough;

a piston rod projecting from said piston through the opposite end ofsaid housing;

means on the outer end of said piston rod for operative relation to theother of said structures; and

means normally hydraulically substantially locking said piston andcylinder to restrain said movement in one direction until apredetermined hydraulic pressure is generated in said cylinder,comprising:

a poppet valve member relatively reciprocably mounted across saidpassageway in said piston,

means normally holding said valve member in position to close saidpassageway,

axially extending and radially facing confronting relatively slidablyengaged control surfaces on said valve member and said piston having alimited range of axial engagement and normally blocking flow throughsaid passageway when said valve is in closed position, and

relatively oppositely axially facing differential area surfaces on saidpiston and said valve member exposed to hydraulic fluid pressuregenerated in said fluid cylinder and said passageway, said valve holdingmeans being responsive to said predetermined hydraulic fluid pressureexerted against said differential area surfaces to allow relative axialmovement of the valve member toward said piston area surface to separatesaid control surfaces and thereby open said passageway.

9. A hydraulic buffer according to claim 8, in which said piston rod ishollow to adjacent its outer end, and said valve holding meanscomprising at least in part a spring stem extending fixedly from saidvalve member through the hollow piston rod and fixedly anchored to thepiston rod adjacent to said outer end and being yieldable in response tosaid predetermined hydraulic fluid pressure exerted against saiddifferential area surfaces in allowing said relative axial movement ofthe valve member and the piston.

10. A hydraulic buffer according to claim 9, in which said spring stemcomprises a tube of substantially smaller wall section than the wallsection of said piston rod, and said piston rod is also yieldable undersaid predetermined hydraulic fluid pressure exerted against saiddifferential area surfaces but in the opposite direction from said sternin the operation of said automatically responsive means.

11. A hydraulic buffer according to claim 10, in which said stem servesas a hydraulic fluid reservoir.

12. A hydraulic buffer according to claim 11, in which said stern hasadjacent to its anchored end a drain passage between the reservoirtherein and the area between the stem and the piston rod, and meansreinforcing the stem in the area of the drain passage.

13. A hydraulic buffer according to claim 1.1, in which said housing hasa reservoir outside of said cylinder, and a fluid conduit meansconnecting the stem reservoir and said housing reservoir.

14. A hydraulic buffer according to claim 13, in which said connectingmeans comprise a return tube extending slidably through said valvemember and having an end portion secured to said housing, with a passageconnecting said end portion with said housing reservoir.

15. A hydraulic buffer according to claim 14, having a check valvedreplenishing connection between said connecting passage and the interiorof said cylinder.

16. A hydraulic buffer of the type to be mounted between two structuressubject to movement toward and away from each other and which movementshould be resisted in at least one direction, comprising:

means defining a housing having opposite ends and provided therein witha hollow hydraulic fluid cylinder between said ends;

a piston reciprocably mounted in said cylinder and having fluid transferpassageway therethrough;

a piston rod projecting from said piston through the opposite end ofsaid housing; means normally hydraulically substantially locking saidpiston and cylinder to restrain said movement in one direction until apredetermined hydraulic pressure is generated in said cylinder,comprising valve means normally blocking hydraulic fluid transferthrough said passageway throughout a substantial working pressure range,and means automatically responsive to said predetermined hydraulicpressure to open said valve means; push-pull swivel connection means onan outer end of said housing opposite to said piston rod for connectionto one of said structures and having an annular concave surface on saidouter end and a member carried by said outer end and spaced from saidsurface having a complementary convex annular surface confronting saidconcave surface; and

push-pull swivel connection means on the outer end portion of saidpiston rod for connection to the other of said structures including aconcave end surface on said rod and a member .mounted on said endportion and having a complementary annular convex surface facing in theopposite direction from said concave end surface.

17. A hydraulic buffer of the type to be mounted between two structuressubject to movement toward and away from each other and which movementshould be resisted in at least one direction, comprising:

means defining a housing having opposite ends and provided therein witha hollow hydraulic fluid cylinder between said ends;

means on one outer end of said housing for operative association withone of said structures;

a piston reciprocably mounted in said cylinder and having fluid transferpassageway therethrough;

a piston rod projecting from said piston through the opposite end ofsaid housing;

means on the outer end of said piston rod for operative relation to theother of said structures;

means normally hydraulically substantially locking said piston andcylinder to restrain said movement in one direction until apredetermined hydraulic pressure is generated in said cylinder,comprising valve means normally blocking hydraulic fluid transferthrough said passageway throughout a substantial working pressure range,and means automatically responsive to said predetermined hydraulicpressure to open said valve means;

said piston rod being hollow to adjacent its outer end;

said valve means comprising a valve member having a stern extendinglongitudinally through the hollow piston rod and having an end portionadjacent said end of the piston rod;

an anchoring pin extending through the adjacent end portions of thepiston rod and the stem; and

a member for connecting the outer end of the piston rod to said other ofsaid structures mounted on the piston rod in retaining relation to saidpin.

18. A hydraulic buffer of the type to be mounted between two structuressubject to movement toward and away from each other and which movementshould be resisted in at least one direction, comprising:

means defining a housing having opposite ends and provided therein witha hollow hydraulic fluid cylinder between said ends;

means on one outer end of said housing for operative association withone of said structures;

a piston reciprocably mounted in said cylinder and having fluid transferpassageway therethrough;

a piston rod projecting from said piston through the opposite end ofsaid housing;

means on the outer end of said piston rod for operative relation to theother of said structures;

means normally hydraulically substantially locking said pisto? andcylinder to restrain said movement in one direction until apredetermined hydraulic pressure is generated in said cylinder,comprising valve means normally blocking hydraulic fluid transferthrough said passageway throughout a substantial working pressure range,and means automatically responsive to said predetermined hydraulicpressure to open said valve means;

a bore in said piston rod extending from said piston to adjacent theouter end of the piston rod;

a valve stem extending from said valve means through said bore andhaving an outer end adjacent to said outer end of the piston rod;

an anchoring pin extending through said piston rod and said stem;

a protective boot about said piston rod having one end attached to saidhousing and having its opposite end adjacent to said one end of thepiston rod; and

means securing said opposite end of the boot to the piston rod andretaining said pin against displacement.

19. A hydraulic buffer of the type to be mounted between two structuressubject to movement toward and away from each other and which movementshould be resisted in at least one direction, comprising:

means defining a housing having opposite ends and provided therein witha hollow hydraulic fluid cylinder between said ends;

means on one outer end of said housing for operative association withone of said structures;

a piston reciprocably mounted in said cylinder and having fluid transferpassageway therethrough;

a piston rod projecting from said piston through the opposite end ofsaid housing;

means on the outer end of said piston rod for operative relation to theother of said structures;

means normally hydraulically substantially locking said piston andcylinder to restrain said movement in one direction until apredetermined hydraulic pressure is generated in said cylinder,comprising valve means normally blocking hydraulic fluid transferthrough said passageway throughout a substantial working pressure range,and means automatically responsive to said predetermined hydraulicpressure to open said valve means;

said valve means comprising a valve member operable within said piston;

said passageway extending in part through said piston under the controlof said valve member, and in part extending along the perimeter of saidpiston; and

a ring valve in slideable engagement with the inner cylinder wall,controlling that part of the passage way around the perimeter of thepiston, said valve abutting against a shoulder on the piston therebyclosing said passageway in one direction of relative movement of thepiston and cylinder, and separating from said shoulder thereby openingsaid passageway in the opposite direction of relative movement of thepiston and cylinder.

20. In a hydraulic buffer according to claim 19, said ring valvecomprising a piston ring, the perimeter of the piston having a groovewider than the piston ring and communicating with said passageway in thepiston.

21. A hydraulic buffer according to claim 19, said ring valve havingmeans sealingly engaging the inner wall of the cylinder and sealingmeans separably engageable with the piston and including biasing meansnormally thrusting the ring valve toward the piston.

22. Inahydraulic bufier:

a hydraulic cylinder having an inner cylindrical surface;

a piston reciprocably operable in pressure strokes in said cylinder andhaving a perimeter confronting said surface;

fluid passageway for displacement of hydraulic fluid from one end of thepiston to the opposite end of the piston along and between saidperimeter of the piston and said surface; and

a control valve mounted in said cylinder spaced from one end of thecylinder and attached to the cylinder at said one end and beingseparable from said opposite end of the piston but being in interceptingrelation to said opposite end of the piston when the piston moves towardsaid one end of the cylinder;

said valve having sealing engagement with said cylinder surface andeffecting sealing engagement with said piston when the piston reachesthe valve and thereby blocking flow of fluid along the piston perimeterto stop advance of the piston toward said References Cited UNITED STATESPATENTS 3,150,779 9/1964 Holm 213--8 3,257,000 6/1966 Cope 213433,334,757 8/1967 Peterson 213-8 3,368,698 2/ 1968 Cardwell 213-433,400,833 9/1968 Powell 2138 3,411,635 11/1968 Powell 213-8 3,412,87011/1968 Rollins 2l3-8 DRAYTON E. HOFFMAN, Primary Examiner US. Cl. X.R.

